Why Do Fleas Even Exist? Discover Their Purpose in the Environment

Written by Jorelle Baker
Published: September 14, 2023
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Quick Answer:

  • Fleas are a valuable source of protein for essential vitamins and minerals for predators like birds, fish, amphibians, ants, beetles, spiders, lizards, and snakes.
  • Fleas are a massive contributor to population control in the environment, having been naturally designed to spread disease and decrease the population of other living beings.
  • Water fleas eat algae, yeast, and bacteria in bodies of freshwater.

Fleas are famously known for being a complete nuisance to our way of life. They are near-invisible parasites that feed off humans and our loving pets, spreading diseases and death everywhere they go. It is easy to think of them simply as annoying blood-sucking pests that exist to make human lives harder.

This raises a question: why would nature make such problematic creatures? What purpose do fleas serve to the environment, aside from making other animal’s lives harder? Do they have any positive benefits to the environment?

Fleas are part of the natural order for a reason. Even if they only play a minor role in the ecosystem, it is vital to understand that role and how it affects everything else.

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What Are Fleas?

Flea - Insect, White Background, Cut Out, Insect, Cat Flea

A cat flea is notably known to infect cats, as well as dogs and humans.


Fleas are small insects that survive by feeding on the blood of animals and humans. There are over 2,500 different types of fleas worldwide, with 300 inhabiting the U.S.

Fleas are primarily known for infesting pets and homes, spreading diseases with their bites, and causing irritating symptoms like itching and swelling. Removing fleas from the home can be a big project. Homeowners have to fumigate every nook and cranny to ensure they eradicate every flea and egg. Even if one egg manages to hatch, the infestation can start again.

Fleas in the Environment

Fleas are blood-sucking parasites that cause nothing but trouble for animals and humans worldwide. However, they serve a vital, yet morbid, role in the environment.

Food Source

Fleas are a valuable source of protein for essential vitamins and minerals for predators. Predators that feast on blood-engorged fleas absorb the nutrients in the stolen blood. Animals such as birds, fish, amphibians, ants, beetles, spiders, lizards, and snakes feed on fleas and digest the blood to support a balanced diet.

For instance, when a small snake eats a blood-engorged flea from a deer, the snake absorbs the vital nutrients it needs to stay healthy. Fleas alone are not enough to satisfy a snake’s appetite, but every meal counts in the wild.

A red ladybug sits on a green leaf on a hot and sunny summer day.

Lady bugs are natural predators of fleas, helping to maintain their spread and infestation.


Ladybugs are the flea’s natural enemy in the wild. Ladybugs seek out and target fleas as their primary food source. They can eat over 50 fleas! These blood-filled insects are a nutritious source of vitamins and minerals to keep their shells bright and healthy. Just another reason to love ladybugs!

Population Control

Fleas are a massive contributor to population control in the environment. Morbid as it is, fleas have been naturally designed to spread disease and decrease the population of other living beings.

Fleas can easily infect hosts with several different types of diseases. Animals infested with fleas are unable to handle the strain and die. Disease is one of the main reasons why animals die sooner in the wild than in captivity. Parasites like fleas overwhelm their hosts and reduce the population to keep nature in balance.

For example, deer are known for carrying both fleas and ticks. If there are too many deer in the wild, then they will exhaust the vegetation and greenery. Predators like coyotes, bears, and wolves can only hunt so much before they are full. Disease is a natural way of managing overpopulation in the wild to keep the ecosystem in balance.

Microscopic Clean-Up

Water flea (Moina macrocopa) under microscope view

Water fleas provide a positive benefit to the environment by cleaning freshwater systems.

©tonaquatic/iStock via Getty Images

Not all fleas spread disease and cause general mayhem. Water fleas or Daphnia are aquatic crustaceans that look similar to terrestrial fleas. They are not like normal fleas, as they provide a positive benefit to the ecosystem that humans continually rely on.

Water fleas eat algae, yeast, and bacteria in bodies of freshwater. Their job is to ensure all sources of fresh water like ponds, puddles, lakes, and rivers are clean and free of hazardous germs and microscopic plant growth.

Additionally, water fleas are an easy food source for amphibians, insects, and fish.

Flea Transmitted Diseases

Fleas are born to spread disease and death. To fulfill that job properly, they are equipped with diseases capable of taking down prey hundreds of times larger than themselves.

Bubonic Plague

Northern Grasshopper Mouse (Onychomys Leucogaster)

Mice and rats were blamed for the Bubonic plague, though fleas on the mice actually spread the disease.

©Liz Weber/Shutterstock.com

The Bubonic plague is known historically as “The Black Death.” This disease wiped out nearly two-thirds of the human population during the 1300s. Rats were seen as the primary cause of the plague at the time, but rats were a scapegoat for the real culprits: fleas.

Thanks to the advent of modern medicine, the Bubonic plague is less threatening to humans now. However, the plague is still dangerous in regions of the world with poor hygiene, and animals are very susceptible to it.

Symptoms of the bubonic plague are:

  • Fever
  • Headaches
  • Chills
  • Weakness
  • Swollen lymph nodes
  • Dark markings at the site of flea bite(s)

Murine Typhus

Super macro close up of brown, amber colored flea, Siphonaptera on human skin. It survives as external bloodsucking parasite of mammals and birds.

Fleas leap onto the skin, biting and spreading disease.

©S.Rohrlach/iStock via Getty Images

Murine typhus is a rare disease that fleas transmit through their bites. It is not common for humans to get it, but it is possible if a home is infested with fleas. It lasts for three to seven days and can be treated with antibiotics.

Symptoms of Murine typhus are:

  • High fever
  • Severe headaches
  • Chills
  • Nausea
  • Weakness

Murine typhus shares symptoms with many other illnesses, so it is important to see a medical professional for diagnosis.

Flea Allergies

dog scratching

Dogs experiencing allergies will often scratch themselves, bite, and lick their paws to soothe itching.


Flea allergies develop when animals and humans experience an allergic reaction to flea bites. Depending on the severity of the allergic reaction, medical attention may be required.

Symptoms of flea allergies are:

  • Itching
  • Hair loss
  • Skin inflammation
  • Crusty patches on the skin
  • Restlessness


A couple of wild rabbits playing on the field

Fleas transmit Tularemia to wild rabbits and hares, infecting thousands each year.

©Wirestock Creators/Shutterstock.com

Tularemia is also known as “rabbit fever.” This disease is notably found in rodents such as rabbits, rats, and hares. Tularemia is rare in humans, with the U.S. reporting approximately 100-200 cases each year. Luckily, it is treatable with antibiotics.

Symptoms of Tularemia are:

  • Skin ulcers
  • Swollen and painful lymph nodes
  • Eye inflammation
  • Sore throat
  • Diarrhea
  • Fever
  • Chills
  • Headaches
  • Muscle aches
  • Joint pain
  • Dry cough


Sand Fleas in a Pile

Sand fleas are also known as mole crabs as they burrow into the ground or a host’s feet to lay their eggs.


Tungiasis is a painful condition where sand fleas burrow into the skin of one’s feet to eat and lay their eggs. Sand fleas reside in hot and heavily sandy regions such as beaches or deserts. Reported cases of Tungiasis are low, but those living in impoverished areas and walking around with bare feet have a higher risk of infection.

If infected, a medical professional should be seen immediately. A medical team will remove the flea properly in a sterile environment to avert further bacterial infections.

Symptoms of Tungiasis are:

  • Intense pain and itching
  • Difficulty walking, sleeping, and concentrating
  • White marks on feet where the flea has burrowed

Fleas are a nuisance. They are an unwanted infestation that infects your pets, your home, and your personal space as they feed on blood. However, they also provide a healthy component to the environment. Without fleas, animals such as rabbits, hares, deer, and other herbivores would overpopulate, causing insurmountable harm to the ecosystem. Despite being pests, fleas serve a vital role in the ecosystem.

The photo featured at the top of this post is © The noob ph/Shutterstock.com

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About the Author

Jorelle Baker is a writer at A-Z Animals, primarily covering pet care, fun facts about animals, and how humans and animals coexist together. He has been writing for his entire life, graduating William Paterson University with a Bachelor's degree in creative writing. He continued his studies at Animal Behavior College to work with animals at grooming salons and veterinary clinics. Jorelle lives in New Jersey and enjoys studying animals in myths and folklore with his cat Kana.

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